JoumalofFluorrne Chemistry 42(1989) 163-172 163

Received February 18 1988 accepted September9 1988

THE PREPARATION OF PmTAFLUOROPHENYL ANTIMONY(II1) AND

ANTIMONY(V) HALIDES AND MIXED HALIDES

PREM RAJ* , A K AGGARWAL and A K SAXENA

Department of Chemistry, Lucknow Unlverslty, Lucknow 226007 (India)

SUMMARY

(C6F5)3Sb (I) has been found to undergo redistribution

reactions with SbC$ in 2/l and l/2 molar ratios to give

quantitative yields of (C6FT)2SbC1 (II) (C6Fg)SbC12 (III),

respectively. Oxidatlve chlorination of ice cold solutions

of (II) and (III) gave (C6Fg)2SbC1j (IV) and (C6Fg)SbC14 (V),

respectively. Bromination of (II) and (III) at - 178OC

yielded mixed halldes, (C6F5),SbC13,Br2 (n = 1 & 2).

INTRODUCTION

In sharp contrast to well documented organo-substituted

antimony(III), RnSbC13_n and antimony(V) halides, RnSbClg_n

(n - 1 or 2) based on hydrocarbon ligands [l-31, those contalnlng

pentafluorophenyl groups are virtually unknown and are

restricted to tris(pentafluorophenyl)antuaony(V) compounds

eg. (C6Fs>+3bX2 (X=C1,Br,NO~,C104,0CH~)[4,51 and C6F513SbIY

(Y - C1,Br,N3, NC0 etc) [61 This 1s probably because the

various methods employed in the preparation of parallel

phenyl antimony(II1) halides are not easy and the reactions

0022 1139/89/$3 50 0 Elsevler Sequola/Pnnted m The Netherlands

164

proceed in low yield [1,21. Our interest in the synthesis

and chemical behaviour of pentafluorophenylantimony(V)

derivatives led us to develop a rapid and facile route for

pentafluorophenyl antimony(III), (C6F5)nSbC1(3_n) (n - 1 & 2)

and antimony(V) chlorides (C6F5),SbC15_, (n = 1 81 2) and

mixed halides, (C6F3)nSbC13_n 2 Br in high yield and high purity.

RESULTS AND DISCUSSION

Pentafluorophenyl antimony(II1) and antimony(V) chlorides

and mixed halides

In the absence of solvent, tris (pentafluorophenyl)

antimony(II1) undergoes a facile redistribution reaction

with antimony trichloride in 2/l and l/2 molar ratiosunder

oxygen free dry atmospheres.

2(C6F5)3Sb + SbC13 --> 3(CgF5)2SbCl

(II)

(C6F&'b + 2SbC13 4 3(C6FS)SbC12

(III)

(1)

(2)

The redistribution is ccmplete in CL. 3h. The

resulting (C6F5)nSbC13_n derivatives are viscous oils which

solidify on standing.

Pentafluorophenylantimony chlorides serve as useful

intermediates for obtaining pentafluorophenylantimony(V)

chlorides or mixed halides. Thus bis(pentafluoropheny1)

165

antimony trichlorlde, (C6F5)2SbC13 can be prepared, as a

white crystalline solid on treatment of (C6F5)2SbC1

with dry chlorine in cold dichloromethane.

(C6F&SbC1 + Cl2 --j(C6F,&SbC13

(IV)

(3)

Similarly, (C6F5)SbC12 is readily converted to the

Sb(V) derivative, (C6F5)SbC14.

(C6FS)SbC12 + C12--_j (C6F5)Sw14

(V)

(4)

Unlike Ph5bC14 which is hygroscopic, (C6F5)SbC14

is remarkably stable at room temperature and not

affected by oxygen.

Oxidative bromination of (C6Fg),SbC13_, leads to

the formation of (C6F5),Sb(V)C13_,Br2

(C6F5)$bC1 + Br2+(C6F5)2SbC1Br2

(VI)

(C6F5)SbC12 + Br2+(C6F5)SbC12Br2

(VII)

(5)

(6)

In view of the reported low stability of antimony(V)

derlvatlves (C6F5)SSbBr2[4], which tend to decompose at room

temperature with the elimination of bromine in solution,

reactions of (pentafluorophenyl)antimony(III) chlorides

with bromine were carried out at low temperature, -17WC

166

(to prevent the possibility of decomposition of bromo

derivative). However, on allowing the reaction mixture

to come to room temperature, no decomposition of

(C6F5)$bC1Br, or (C6F5)SbC12Br2 was observed. Both the

halides were obtained in high yield.

IR spectroscopy

All the isolated compounds (II-VII) exhibit

characteristic IR absorptions due to C6F5 groups attached

to an Sb atom and are in conformity with the reported

literature values [4,6]. The IR spectra of tris(pentafluoro-

phenyl)antimony and its dihalides have previously been

described[S]. The comparison of these data with phenyl

analogues has enabled identification of prominent IR

absorption for the compounds (II) to (VII) which are

listed in Table 1.

The stretching vibrations of the (Sb-X) groups

occur:: at higher frequencies than for the corresponding

phenyl derivatives. The replacement of the hydrocarbon

groups by the highly electron withdrawing pentafluorophenyl

groups leads to an increase in the partial positive charge

on the antimony atom. This in turn could result in a

contraction of the orbital used by antimony to bond to

the halogen, leading to a stronger bond and higher

vibrational frequency.

TABLE

1

Relevant

infrared

frequencies

of (Pentafluorophenyl)antlmony

(III) e(v)

derlvatlves

In cm-')*

R2SbCl

RSbC12

R2SbC13

RSbC14

R2SbC)Br2

RSbC12Br2

Assignments

219(

ms)

290(

w)

340(

m)

448(w)

;;:[: 1

604(m)

713(m)

778(m)

956(

vs)

220(w)

225(ms)

287(w)

287(w)

339(ms)

325(s)

45O(vw)

447(vw)

593(mw)

594(w)

6Wm

) 620(ms)

715(m)

725(m)

779(ms)

761(m)

228(s

230(m

_ I

288(mw)

335(vs)

445(ww)

596(mw)

625(m

)

729(ms)

762 mw

t I

759 mw

98O(ws)

222(m)

235(vs)

287(mw)

322(m)

446(w)

621(ms)

728(m)

749(mw

751(mw 1

99O(ws)

224(m)

231(vs)

285(w)

323(ms)

446(vw)

596(w)

615(ms)

722(ms)

75O(mw)

d,t

Sb-Br

t

Sb-Cl

Y

P

r S

V

+ smstrong, m=medium, w=weak, v=very

168

The spectra of all the chlorides show a band between

320-340 cm-' increasing ,in intensity with increasing chlorine

content, which can be attributed to one of the antimony

chlorine stretching modes. In the case of (C6F5)2SbC1Br2

and (C6F5) SbC12Br2 a strong band at 235 + 5 cm -1 may be

assigned to antimony-bromine stretching vibrations.

EXPERIMENTAL

Pentafluorobromobenzene (Imperial Smelting Company,

Bristol) was used as received. Antimony trichloride (Fluka)

was dried over P40,0 and sublimed before use. Tris (Penta-

fluorophenyl)antimony was prepared as described previously [71.

All the solvents were purified and dried by

standard procedures and the reactions carried out under

anhydrous conditions.

Infrared spectra were recorded in the range

4000-200 cm" by using KBr/CsI pellets on a Perkin-Elmer-

577 spectrophotometer. Antimony and chlorine were

determined as reported earlier [4,6].

Typical experimental details of the reactions are

described below. Analytical data are given in Table 2.

Bis(pentafluorophenyl)antimony(III)chloride Antimony

trichloride (2.28 g, 10 mmol) and tris(pentafluoropheny1)

antimony (12.45 gm, 20 mmol) were heated at 60-70°C in

absence of solvent for about 3 hrs. Cooling yielded white

TABLE 2

Analytlcal data for PentafluorophenylantImony(II1) & (V) derlvatlves

Compound

Molecular

Analysis Calcd (Found) in 96

formula

C

Sb

Cl

II

III

IV

V

VI

VII

C6F5SbC12

C6F5SbC14

79-8

0 29

.50

(29.

31)

80-81

20.3

5 (2

0.01

)

248

25.8

2 (2

5.61

)

236-

7 16

.96

(16.

71)

206

C6F5SbBr2C12

214

21.9

0 (2

2.11

)

24.3

5 (2

4.77

) (E

2)

33.4

1 19

.33

(33.

83)

(19.

73)

21.1

0 18

.65

(21.

64)

(18.

94)

28.0

5 32

.50

(28.

25)

(32.

96)

18.2

0 -

(18

68)

13.5

6 23

.00

- (1

3.85

) (2

3.41

)

170

crystals, which on recrystallisation from dichloromethane

gave the pure compound (yield 11.78 gm, 80%).

(Pentafluorophenyl)antlmony(III)dlchlor~de Antimony

trichloride (4.56 gm, 20 mmol), and trls(pentafluoropheny1)

antimony (6.22 gm, 10 mmol) were heated at about 60-70°C

m absence of solvent for about 3 hrs. Cooling yielded

white crystals, which on recrystallisatlon from dlchloro-

methane gave the pure compound, (yield - 8.0 gm, 75%).

Bis(pentafluorophenyl)antimony(V)trichloride B1.s

(pentafluorophenyl)antimony(III)chlorlde (4.9 gm, IO mmol)

was dissolved in dichloromethane (100 cm3) and cooled to

O°C in ice. Dry chlorine (0.71 g, IO mmol) was then added

from a weighed trap and the temperature was allowed to rise

Slowly to room temperature On concentration of solution,

white crystals were obtained which on recrystallisation

from dlchloromethane or petroleum ether (40-6OoC) gave

the pure compound. (Yield 3.9 gm, 70%).

(Pentafluorophenyl)antlmonyotetrachlor~de Penta-

fluorophenyl antimony(II1) dichloride (3.6 gm, 10 mmol)

dissolved in dichloromethane (100 cm3) was ice cooled

with ice. Dry chlorine (0.71 gm, 10 mmol) was then added

from a weighed trap and the temperature was then added

rise slowly to rocm temperature. On concentration of the

171

solution white crystals were obtained which on

recrystallisation from dichloromethane/petroleum ether

(40-600) gave the pure compound (Yield 3 gm, 70%).

Bls(pentafluorophenyl)antlmony chloride dlbromlde

Anhydrous Br2 (1.6 gm, 10 mmol) was condensed at -178OC

into a solution of bis(pentafluorophenyl)antimony(III)

chloride (4.9 gm, 10 mmol) in dichloromethane (100 cm3).

After allowing the temperature to rise slowly on concentrating

the solution the compound separated on coolmg. Recrystallisa-

tion from dichloromethane afforded the pure product

(Yield 5.5 gm, 85%).

(Pentafluorophenyl)antimony(V)dichloridedibromide

Anhydrous bromine (1.6 gm, 10 mmol) was condensed at

-178oC into a solution of (pentafluorophenyl)antimony(III)

dichloride (3.6 gm, 10 mmol) in dichloromethane (100 cm3).

After allowing the temperature to rise slowly on concentrating

the solution the compound separatedon cooling Recrystalll-

satlon from dlchloromethane produced the pure product

(Yield 4.3 gm, 83%).

ACKNOWLEDGEMENT

The authors are thankful to the Council of Scientific

& Industrial Research, New Delhi for financial assistance,

the Head of the Chemistry Department, Lucknow University

for providing necessary laboratory facilities and the

Director, RSIC, Lucknow for obtaining IR spectra and

microanalysis.

172

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1 G.O. Doak, L.D. Freedman 'Organometallic Compounds of

Arsenic, Antimony and Bismuth' Wiley-Interscience,

New York (1970).

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M.T.P. International Review of Science, H.J. Emel6us and

B.J. Aylett (eds.) Vol.+, P.383, Butterworths,

London (1972).

3 J.L. Wardell in G. Wilkinson ted.1 'Arsenic, Antimony and

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